///
// * jdbm LICENSE v1.00
// *
// * Redistribution and use of this software and associated documentation
// * ("Software"), with or without modification, are permitted provided
// * that the following conditions are met:
// *
// * 1. Redistributions of source code must retain copyright
// *    statements and notices.  Redistributions must also contain a
// *    copy of this document.
// *
// * 2. Redistributions in binary form must reproduce the
// *    above copyright notice, this list of conditions and the
// *    following disclaimer in the documentation and/or other
// *    materials provided with the distribution.
// *
// * 3. The name "jdbm" must not be used to endorse or promote
// *    products derived from this Software without prior written
// *    permission of Cees de Groot.  For written permission,
// *    please contact cg@cdegroot.com.
// *
// * 4. Products derived from this Software may not be called "jdbm"
// *    nor may "jdbm" appear in their names without prior written
// *    permission of Cees de Groot. 
// *
// * 5. Due credit should be given to the jdbm Project
// *    (http://jdbm.sourceforge.net/).
// *
// * THIS SOFTWARE IS PROVIDED BY THE ndbm PROJECT AND CONTRIBUTORS
// * ``AS IS'' AND ANY EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT
// * NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
// * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL
// * CEES DE GROOT OR ANY CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
// * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
// * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
// * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
// * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
// * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
// * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
// * OF THE POSSIBILITY OF SUCH DAMAGE.
// *
// * Copyright 2000 (C) Cees de Groot. All Rights Reserved.
// * Contributions are Copyright (C) 2000 by their associated contributors.
// *
// * $Id: PageHeader.java,v 1.2 2003/09/21 15:47:01 boisvert Exp $
// 


//*************************************************************************
//**  Included in JDMB 1.0 port to SharpDBM;  11/2013 Cyrus Neah cneah@codingreal.com
//**  SharpDBM is an independent reimplementation of the JDBM 1.0 software library in C#  
//*************************************************************************


using SharpDBM.helper;

namespace SharpDBM.recman
{

///
// *  This class represents a page header. It is the common superclass for
// *  all different page views.
// 
	public class PageHeader : BlockView
	{
	// offsets
		private const short O_MAGIC = 0; // short magic
		private const short O_NEXT = Magic.SZ_SHORT; // long next
		private const short O_PREV = O_NEXT + Magic.SZ_LONG; // long prev
		protected internal const short SIZE = O_PREV + Magic.SZ_LONG;

	// my block
		protected internal BlockIo block;

//    *
//     *  Constructs a PageHeader object from a block
//     *
//     *  @param block The block that contains the file header
//     *  @throws IOException if the block is too short to keep the file
//     *          header.
//     
		public  PageHeader(BlockIo block)
		{
			initialize(block);
			if (!magicOk())
				throw new Error("CRITICAL: page header magic for block " + block.getBlockId() + " not OK " + getMagic());
		}

//    *
//     *  Constructs a new PageHeader of the indicated type. Used for newly
//     *  created pages.
//     
        public PageHeader(BlockIo block, short type)
		{
			initialize(block);
			setType(type);
		}

//    *
//     *  Factory method to create or return a page header for the
//     *  indicated block.
//     
		public static PageHeader getView(BlockIo block)
		{
			BlockView view = block.getView();
			if (view != null && view is PageHeader)
				return (PageHeader) view;
			else
				return new PageHeader(block);
		}

		private void initialize(BlockIo block)
		{
			this.block = block;
			block.setView(this);
		}

//    *
//     *  Returns true if the magic corresponds with the fileHeader magic.
//     
		private bool magicOk()
		{
			int magic = getMagic();
			return magic >= Magic.BLOCK && magic <= (Magic.BLOCK + Magic.FREEPHYSIDS_PAGE);
		}

//    *
//     *  For paranoia mode
//     
		protected internal virtual void paranoiaMagicOk()
		{
			if (!magicOk())
				throw new Error("CRITICAL: page header magic not OK " + getMagic());
		}

	/// Returns the magic code 
		internal virtual short getMagic()
		{
			return block.readShort(O_MAGIC);
		}

	/// Returns the next block. 
		internal virtual long getNext()
		{
			paranoiaMagicOk();
			return block.readLong(O_NEXT);
		}

	/// Sets the next block. 
		public virtual void setNext(long next)
		{
			paranoiaMagicOk();
			block.writeLong(O_NEXT, next);
		}

	/// Returns the previous block. 
        internal virtual long getPrev()
		{
			paranoiaMagicOk();
			return block.readLong(O_PREV);
		}

	/// Sets the previous block. 
		internal virtual void setPrev(long prev)
		{
			paranoiaMagicOk();
			block.writeLong(O_PREV, prev);
		}

	/// Sets the type of the page header 
		public virtual void setType(short type)
		{
			block.writeShort(O_MAGIC, (short)(Magic.BLOCK + type));
		}
	}

}